1. Field of the Invention
This invention relates to a technique for determining a flow-down state of liquid flowing down from a nozzle located above a work toward the upper surface of the work.
2. Description of the Related Art
In a technique in which processing is performed by supplying liquid to a processing object (work) such as a substrate, it is necessary in some cases to monitor whether or not a predetermined amount of the liquid is supplied at a predetermined timing. A technique for determining a discharged state of liquid discharged from a nozzle is, for example, described in each literature below.
In a technique described in JP2002-316080A, a discharge port of a nozzle is imaged by a camera. Further, a background plate is provided at a position equivalent to the background of the nozzle when viewed from the camera and a moment of starting the discharge is detected by a change in shading appearing in an image. Further, a technique described in JP2009-095826A is a technique for inspecting a nozzle, and optically detects a thickness of a liquid column discharged in a column-like manner from the nozzle. Specifically, reflected light of light irradiated toward the liquid column is imaged, a discharge amount (thickness of the liquid column) is determined from a luminance average value of an image and the presence or absence of a variation of the discharge amount is determined from a luminance variation amount. Further, in a technique described in JP2012-009812A, a liquid column which becomes luminous by the reflection of illumination light by the liquid column is imaged. The presence or absence of the discharge, a discharge amount and the like are determined by comparing that image and reference information prepared in advance.
In each of the above conventional techniques, the discharge is determined utilizing a change of the content of an image to be imaged depending on the presence or absence of the discharge. However, since the processing is required to be even faster, it has been difficult to utilize such determination techniques. For example, in a configuration in which the discharge of liquid is started after a movable nozzle is positioned at a predetermined position, the start of the discharge of the liquid can be detected by detecting a change between a reference image after the positioning of the nozzle and before the discharge of the liquid and an image after the start of the discharge. In contrast, it has also become necessary in recent years to discharge liquid substantially during a movement of a nozzle or simultaneously with the completion of positioning. In such a configuration, it is difficult to prepare a reference image to be compared. Further, a liquid discharge time has also become shorter for faster processing and the saving of processing liquid.
Thus, a technique is required which can reliably determine a state of liquid from an image imaged at a certain time without depending on a comparison with an image before or after the former image or a reference image.